Thin film piezoelectric element, method of manufacturing the same, and actuator

ABSTRACT

Two piezoelectric thin films each sandwiched between a main electrode layer and an opposite electrode layer are laminated in pairs to form a thin film piezoelectric element. An electrode leading area has a region in which the main electrode layer partially projects from the piezoelectric thin film, and another region in which only an insulating layer is formed on a part of the opposite electrode layer. At least one of a first opening formed through the insulating layer in the former region and a second opening formed through the insulating layer in the latter region is provided. Formed via the opening is a connection wiring for connecting to the opposite electrode layer or the main electrode layer and leading to the surface layer.

FIELD OF THE INVENTION

[0001] The present invention relates to a thin film piezoelectric element, a method of manufacturing the element, and an actuator using the element.

BACKGROUND OF THE INVENTION

[0002] In recent years, efforts have been made to realize micro machinery using technologies for manufacturing semi-conductors. Mechanical electric elements, such as an actuator, are getting into the limelight. The use of such elements can realize small and high-precision machinery. Especially examined are applications of an actuator using piezoelectric elements to micro positioning of the head slider of a disk drive.

[0003] For instance, in a magnetic disk recording/reproducing device, the magnetic head for recording into or reproducing from a magnetic disk is mounted on the head slider and attached to the actuator arm. This actuator arm is rocked by the voice coil motor (hereinafter referred to as a “VCM”) to position the magnetic head in a specific track position on the magnetic disk for recording and reproduction. However, with improvement of recording density, sufficient precision cannot be ensured by such conventional positioning only using a VCM. For this reason, proposed in addition to the positioning means using a VCM is a technique for driving the head slider for high-speed and high-precision positioning with a micro positioning means using piezoelectric elements. (“Switching to super-high TPI and piggy-back actuator”, IDEMA Japan News, International Disk Drive Equipment Material Association Japan, September, 1999, Vol. 32, pp4-7)

[0004] As described above, actuators using piezoelectric elements are expected to find a wide range of applications. As disclosed in the Japanese Patent Unexamined Publication No. H06-22448, many of the conventional piezoelectric elements are structured to be laminated by a green sheet lamination method or thick film multilayer method. However, when the piezoelectric elements are produced by these manufacturing methods, the thickness of one layer of the piezoelectric elements measures several dozens micro meters. Thus, a drive voltage of at least 100V is necessary.

[0005] In contrast, shown in the Japanese Patent Unexamined Publication No. H08-88419 are a thin film laminated actuator that is small and capable of being driven at a low voltage and has a large amount of displacement, and a method of manufacturing the actuator. The manufacturing method is described hereinafter. First, formed on a single-crystal substrate made of magnesium oxide (MgO), strontium titanate (SrTiO₃), sapphire (Al₂O₃) or other material are an electrode layer made of platinum (Pt), aluminum (Al), gold (Au), silver (Ag) or other material, a piezoelectric layer made of piezoelectric material including lead zirconium titanate (PZT), lead lanthanum zirconate titanate (PLZT), and an electrode layer made of the above-mentioned material. On these layers, an adhesive layer made of glass or silicon is formed to provide a piezoelectric member.

[0006] Thereafter, the two piezoelectric members are joined via the adhesive layers by an anode junction method. Then, one of the substrates is removed by grinding or other method. After the removal, another adhesive layer is formed on the exposed electrode layer again. This adhesive layer and the adhesive layer of another piezoelectric member are joined again. By repeating these steps, multilayered laminate is formed. Thereafter, by alternately leading the inner electrodes in this laminate from both sides to provide a laminated actuator.

[0007] Such a thin film laminated actuator features an inexpensive power supply circuit because the drive voltage is low. However, because external electrodes are formed from the two side faces of a laminate of multilayered piezoelectric members via insulating layers, the external electrodes must be formed for each laminate. This poses a problem in mass production. Additionally, because this actuator is structured so that displacement occurs in the direction perpendicular to the surface of the substrate, the shape of the actuator is not suitable as a micro-actuator for the head slider of a disk drive, for example.

SUMMARY OF THE INVENTION

[0008] The present invention aims to improve the reproducibility of the shape of piezoelectric elements in etching, prevent failures, e.g. short circuits between the electrodes sandwiching a piezoelectric thin film, and provide a thin film piezoelectric element having excellent piezoelectric characteristics and few variations and a method of manufacturing the piezoelectric element, and an actuator using the piezoelectric element.

[0009] According to one aspect of the present invention, there is provided a thin film piezoelectric element including:

[0010] a structure in which a first piezoelectric thin film sandwiched between a first main electrode layer and a first opposite electrode layer and a second piezoelectric thin film sandwiched between a second main electrode layer and a second opposite electrode layer are coupled so that the first opposite electrode layer and the second opposite electrode layer are opposed and physically and electrically connected to each other; and

[0011] an insulating layer covering the outer periphery along the thickness of the structure.

[0012] The first main electrode layer in an electrode leading area has a first main electrode layer projection partially extending from the first piezoelectric thin film. A first connection wiring for connecting the first main electrode layer projection and the second main electrode layer is disposed via a first opening formed through the insulating layer on the first main electrode layer projection.

[0013] The second main electrode layer, the second piezoelectric thin film, and the second opposite electrode layer in the electrode leading area are formed narrower than the first opposite electrode layer to provide a region in which the insulating layer is provided on the first opposite electrode layer. A second connection wiring for electrical connection to the first opposite electrode layer is provided via a second opening formed through the insulating layer in this region.

[0014] According to another aspect of the present invention, there is provided a thin film piezoelectric element including:

[0015] a pair of element parts disposed in a plane with a predetermined space held therebetween, a piezoelectric function area working as a piezoelectric body of the pair of element parts having mirror images symmetrical with respect to the centerline of the predetermined space; and

[0016] a joint for coupling the element parts in a part of the predetermined space, the joint made of at least one kind of material comprising the element parts.

[0017] Each of the element parts includes:

[0018] a structure in which a first piezoelectric thin film sandwiched between a first main electrode layer and a first opposite electrode layer and a second piezoelectric thin film sandwiched between a second main electrode layer and a second opposite electrode layer are coupled so that the first opposite electrode layer and the second opposite electrode layer are opposed and physically and electrically connected to each other; and

[0019] an insulating layer covering the outer periphery along the thickness of the structure.

[0020] The first main electrode layer of an electrode leading area has a first main electrode layer projection partially projecting from the first piezoelectric thin film. The second main electrode layer, the second piezoelectric thin film, and the second opposite electrode layer in the electrode leading area are formed narrower than the first opposite electrode layer to provide a region in which the insulating layer is provided on the first opposite electrode layer. At least one of a first opening formed through the insulating layer on the first main electrode layer projection or a second opening formed through the insulating layer on the first opposite electrode layer in this region is provided. A connection wiring connecting to the first opposite electrode layer or the first main electrode layer and leading to a surface layer is provided via the first opening or the second opening.

[0021] With this structure, only the insulating layer needs to be etched after the two piezoelectric thin films are joined. This facilitates etching and improves the accuracy of pattern shapes. Additionally, because openings do not need to be formed through piezoelectric thin films, failures, such as short circuits between the electrodes sandwiching the piezoelectric thin films, can be prevented.

BRIEF DESCRIPTION OF THE DRAWINGS

[0022]FIG. 1 is a plan view of an actuator using a thin film piezoelectric element made of a pair of element parts in accordance with a first exemplary embodiment of the present invention.

[0023]FIG. 2 is a drawing for describing an idea of the operation of the actuator.

[0024]FIG. 3 is a perspective view of an essential part of a magnetic disk recording/reproducing device using the actuator.

[0025]FIG. 4 is a drawing for illustrating a sectional structure of the actuator taken along line 100-100 of FIG. 1.

[0026]FIG. 5A is a sectional view showing a first main electrode layer and a first piezoelectric thin film are laminated on a first substrate and then the first piezoelectric thin film is etched, in a method of manufacturing a thin film piezoelectric element in accordance with the first exemplary embodiment of the present invention.

[0027]FIG. 5B is a sectional view showing the first main electrode layer is etched, in the manufacturing method.

[0028]FIG. 5C is a sectional view showing a first opposite electrode layer is formed on the first piezoelectric thin film, in the manufacturing method.

[0029]FIG. 5D is a plan view showing the first opposite electrode layer is formed on the first piezoelectric thin film, in the manufacturing method.

[0030]FIG. 6A is a sectional view showing a second main electrode layer and a second piezoelectric thin film are laminated on a second substrate and then the second piezoelectric thin film is etched, in the manufacturing method.

[0031]FIG. 6B is a sectional view showing the second main electrode layer is etched, in the manufacturing method.

[0032]FIG. 6C is a sectional view showing a second opposite electrode layer is formed on the second piezoelectric thin film, in the manufacturing method.

[0033]FIG. 6D is a plan view showing the second opposite electrode layer is formed on the second piezoelectric thin film, in the manufacturing method.

[0034]FIG. 7A is a sectional view showing the first opposite electrode layer and the second opposite electrode layer are joined to each other, in the manufacturing method.

[0035]FIG. 7B is a sectional view showing a gap is filled with an insulating resin layer, in the manufacturing method.

[0036]FIG. 7C is a sectional view showing the second substrate is removed by etching, an insulating protective coat is formed, and predetermined holes are provided, in the manufacturing method.

[0037]FIG. 8A is a sectional view showing the insulating resin layer is etched to a shape covering a structure, in the manufacturing method.

[0038]FIG. 8B is a sectional view showing first connection wirings and second connection wirings are formed, in the manufacturing method.

[0039]FIG. 8C is a sectional view showing the thin film piezoelectric element is removed from the substrate, in the manufacturing method.

[0040]FIG. 9 is a plan view of a thin film piezoelectric element in accordance with a second exemplary embodiment of the present invention.

[0041]FIG. 10 is a sectional view of the thin film piezoelectric element in accordance with the second exemplary embodiment.

[0042]FIG. 11A is a sectional view showing a first main electrode layer and a first piezoelectric thin film of predetermined patterns are laminated on a first substrate, in a method of manufacturing a thin film piezoelectric element in accordance with the second exemplary embodiment.

[0043]FIG. 11B is a sectional view showing a first opposite electrode layer is further formed on the first piezoelectric thin film, in the manufacturing method.

[0044]FIG. 11C is a plan view showing the first opposite electrode layer is further formed on the first piezoelectric thin film, in the manufacturing method.

[0045]FIG. 12A is a sectional view showing a second main electrode layer and a second piezoelectric thin film of predetermined patterns are laminated on a second substrate, in the manufacturing method.

[0046]FIG. 12B is a plan view showing the second main electrode layer and the second piezoelectric thin film of the predetermined patterns are laminated on the second substrate, in the manufacturing method.

[0047]FIG. 13A is a sectional view showing the first opposite electrode layer and the second opposite electrode layer are joined to each other, the second substrate is removed by etching, and an insulating protective coat is further formed, in the manufacturing method.

[0048]FIG. 13B is a sectional view showing first connection wirings and a second connection wiring are formed, in the manufacturing method.

[0049]FIG. 14 is a sectional view of a thin film piezoelectric element in accordance with a modification of the second exemplary embodiment of the present invention.

[0050]FIG. 15 is a sectional view of an electrode leading area of a thin film piezoelectric element in accordance with a third exemplary embodiment of the present invention.

[0051]FIG. 16A is a sectional view showing a first main electrode layer, a first piezoelectric thin film, and a first opposite electrode layer are laminated on a first substrate to form predetermined patterns, in a method of manufacturing a thin film piezoelectric element in accordance with the third exemplary embodiment.

[0052]FIG. 16B is a plan view of a shape shown in FIG. 16A.

[0053]FIG. 17A is a sectional view showing a second main electrode layer, a second piezoelectric thin film, and a second opposite electrode layer are laminated on a second substrate, in the method of manufacturing a thin film piezoelectric element in accordance with the third exemplary embodiment.

[0054]FIG. 17B is a plan view of a shape shown in FIG. 17A.

[0055]FIG. 18A is a sectional view showing the first opposite electrode layer and the second opposite electrode layer are brought into opposite intimate contact with and joined to each other, the second substrate is removed by etching, and an insulating protective coat is formed on a exposed surface, in the method of manufacturing a thin film piezoelectric element in accordance with the third exemplary embodiment.

[0056]FIG. 18B is a sectional view showing the insulating protective coat and an insulating resin layer are etched, in the method of manufacturing a thin film piezoelectric element in accordance with the third exemplary embodiment.

DETAILED DESCRIPTION OF THE INVENTION

[0057] Thin film piezoelectric elements of exemplary embodiments of the present invention are specifically described hereinafter with reference to the accompanying drawings. Throughout the drawings, same components are denoted with the same reference marks, and thus the description of those components is omitted in some cases.

First Exemplary Embodiment

[0058] Descriptions are provided of thin film piezoelectric element 54, a method of manufacturing the element, and an actuator and disk drive using the element of the first exemplary embodiment of the present invention.

[0059]FIG. 1 shows a plan view of an actuator using thin film piezoelectric element 54 made of a pair of element parts 54A and 54B in accordance with the present invention. This actuator is used to precisely position the recording/reproducing head in specific positions on a disk in various kinds of disk drives.

[0060] This embodiment describes a case where this actuator is used for a magnetic disk recording/reproducing device. In a magnetic disk recording/reproducing device, the actuator is used to jog the head slider having a magnetic head mounted thereon to perform high-precision micro-positioning of the magnetic head in specific track positions on a disk.

[0061] Thin film piezoelectric element 54 shown in FIG. 1 has two element parts 54A and 54B. This pair of element parts 54A and 54B has a relation of mirror images with respect to line 102-102. Further, each of these element parts 54A and 54B is structured of piezoelectric function area 106 mainly working as a piezoelectric body and electrode leading area 108 mainly working for connection to external circuits.

[0062] This pair of element parts 54A and 54B is bonded and fixed to flexure 460, i.e. a supporting member, by an adhesive resin layer (not shown). After bonding, connection electrode pads made of first connection wirings 8 and second connection wirings 9 provided on each of element parts 54A and 54B are connected to electrode pads for piezoelectric element 464 provided on flexure 460 by wire leads 467, for example, to form an actuator for micro-positioning the head.

[0063] Flexure 460 extends from the area having thin film piezoelectric element 54 joined thereto, and has slider supporting member 461 for fixing a head slider (not shown). Provided on this slider supporting member 461 are head electrode pads 462 for connection to the electrode terminals on the magnetic head (not shown) mounted on the head slider (not shown). From these head electrode pads 462, head electrode wirings 463 are routed on flexure between thin film piezoelectric element parts 54 toward connection pads (not shown) to external equipment, like electrode wirings for piezoelectric element 465 routed from electrode pads for piezoelectric element 464.

[0064] The operation of an actuator structured as above is described. When voltages of opposite polarities are applied to a pair of element parts 54A and 54B of thin film piezoelectric element 54, one element part 54A expands and the other element part 54B contracts as illustrated in FIG. 2. The displacement in these two opposite parallel directions effects on slider supporting member 461. Responsive to the resultant force, slider supporting member 461 jogs in the direction of line 104-104. By high-precision control of such jogging, the magnetic head can highly precisely be positioned in predetermined track positions on a disk (not shown). For instance, when the thickness of the piezoelectric thin film of each element part 54A or 54B is 2.5 μm and voltages of ±5V of opposite phases are applied, the amount of displacement of the head in the direction of 104-104 can be made ±0.8 μm.

[0065] A perspective view of an essential part of a magnetic disk recording/reproducing device using this actuator is shown in FIG. 3. Magnetic disk 902 is fixed to main spindle 901, and rotated by rotating means 903 in the direction shown by arrow A at specific revolutions. As the rotating means, a spindle motor is generally used. On a side opposed to magnetic disk 902, suspension arm 906 having a flexure (not shown) is fixed to arm 907. This arm is pivotally supported by bearing 908. Head slider 904 is fixed to the flexure. Further, a pair of thin film piezoelectric element parts 54 is fixed to the flexure, i.e. a supporting member. This flexure and thin film piezoelectric element 54 constitute actuator 905.

[0066] A VCM, first positioning means 909, rocks arm 907 to position head slider 904 in specific track positions on magnetic disk 902. In a conventional magnetic disk recording/reproducing device, positioning is performed only by this first positioning means 909, i.e. the VCM. However, in this embodiment, the above-mentioned actuator 905 further jogs head slider 904 for more highly precise positioning. Because this jogging of actuator 905 can be controlled by voltages applied to thin film piezoelectric element 54, the actuator sufficiently allows the magnetic head to follow minute track positions. This enables further high-density recording and reproduction. The entire parts of the magnetic disk recording/reproducing device are covered with housing 910 and a lid (not shown) to be hermetically sealed from outside air.

[0067] The sectional structure of this actuator is shown in FIG. 4. FIG. 4 shows a sectional shape of the actuator taken along line 100-100 of FIG. 1.

[0068] As obvious from FIG. 1 and the description thereof, thin film piezoelectric element 54 of this embodiment has mirror images symmetrical with respect to line 102-102. Respective element parts 54A and 54B are structured so that first piezoelectric thin film 3 sandwiched between first main electrode layer 2 and first opposite electrode layer 5 and second piezoelectric thin film 13 sandwiched between second main electrode layer 12 and second opposite electrode layer 15 are coupled with first opposite electrode layer 5 and second opposite electrode layer 15 joined and fixed to each other via conductive adhesive layer 20. The outer periphery of the element is protected by insulating layer 6 of the same thickness. On this insulating layer 6 and second main electrode layer 12, insulating protective coat 18 is formed.

[0069] Further, in piezoelectric function area 106 mainly working as a piezoelectric body, first main electrode layer 2, first opposite electrode layer 5, first piezoelectric thin film 3, second main electrode layer 12, second opposite electrode layer 15 and second piezoelectric thin film 13 are all formed into the same shape.

[0070] Insulating layer 6 protects first piezoelectric thin film 3, second piezoelectric thin film 13 and other components, and prevents contact of first connection wiring 8 with first opposite electrode layer 5, second opposite electrode layer 15 and adhesive layer 20 and short circuits therebetween. In this embodiment, because this insulating layer 6 is made of resin material, it is hereinafter referred to as insulating resin layer 6.

[0071] Also in electrode leading area 108, the overall shape of the element is structured so that first piezoelectric thin film 3 sandwiched between first main electrode layer 2 and first opposite electrode layer 5 and second piezoelectric thin film 13 sandwiched between second main electrode layer 12 and second opposite electrode layer 15 are coupled with first opposite electrode layer 5 and second opposite electrode layer 15 physically and electrically connected to each other by conductive adhesive layer 20.

[0072] However, on the outer peripheral sides opposite to the inner peripheral sides where element parts 54A and 54B are opposite to each other, first main electrode layer 2 partially extends and forms first main electrode layer projections 21 projecting from first piezoelectric thin film 3. Formed through insulating resin layer 6 are first openings 62 reaching these first main electrode layer projections 21. Via each of these first openings 62, first main electrode layer projection 21 is electrically connected to second main electrode layer 12 by first connection wiring 8.

[0073] On the other hand, in the inner peripheral sides where element parts 54A and 54B are opposite to each other, second main electrode layer 12, second piezoelectric thin film 13 and second opposite electrode layer 15 are partially notched and formed narrower than first opposite electrode layer 5. This makes a region in which first opposite electrode layers 5 are exposed (hereinafter referred to as “first opposite electrode layer projection 51”). Formed through insulating resin layer 6 are second openings 64 reaching these first opposite electrode layer projections 51. Via each of these second openings 64, second connection wiring 9 connected to first opposite electrode layer 5 is formed to the surface of insulating protective coat 18.

[0074] Because first opposite electrode layer 5 and second opposite electrode layer 15 are joined by conductive adhesive layer 20, second opposite electrode layer 15 is also connected to second connection wiring 9. Joint 70 for coupling two element parts 54A and 54B is formed by insulating resin layer 6 to integrate two parts.

[0075] First connection wirings 8 and second connection wirings 9 also serve as connection electrode pads for connection to electrode pad for piezoelectric elements 64, as shown in FIG. 1. Thus, thin film piezoelectric element 54 is formed.

[0076] This thin film piezoelectric element 54 is bonded and fixed to flexure 460 by adhesive resin layer 458. Materials of this adhesive resin layer 458 include commercially available one-part cold-setting epoxy resin, two-part adhesive, and urethane resin.

[0077] In thin film piezoelectric element 54, a protective coat for protecting first connection wirings 8 and second connection wirings 9 can be formed, and holes can be provided in specific areas to form connection electrode pads. This structure can protect first connection wirings 8 and second connection wirings 9 from external environment, thus further improving the reliability.

[0078] A method of manufacturing thin film piezoelectric element 54 of this embodiment is detailed hereinafter with reference to the drawings. FIGS. 5A through 8D are drawings for illustrating major steps, in a method of manufacturing thin film piezoelectric element 54 of this embodiment. Because thin film piezoelectric element 54 of this embodiment is characterized by the structure of connection wirings for connection to electrode pads for piezoelectric elements 64, the steps are described with reference to a sectional shape taken along line 100-100 of FIG. 1.

[0079] First, formation and processing thin films on first substrate 1 is described with reference to FIGS. 5A through 5D.

[0080]FIG. 5A shows first main electrode layer 2 and first piezoelectric thin film 3 are laminated on first substrate 1 and then this first piezoelectric thin film 3 is etched into a predetermined shape.

[0081] Because excellent piezoelectric characteristics are required of first piezoelectric thin film 3, it is important to select the materials of first substrate 1 and the piezoelectric thin film and conditions for forming them. For example, magnesium oxide single-crystal substrate (MgO substrate) is used as first substrate 1. On this MgO substrate, a c-axis oriented platinum layer (Pt layer) is sputtered as first main electrode layer 2. Thereafter, a lead zirconium titanate (PZT) film, for example, is sputtered on this Pt layer, to provide a thin film having excellent piezoelectric characteristics. Forming this PZT film while the temperature of the MgO substrate is kept at approx. 600° C. can provide a PZT film polarized in the direction perpendicular to the surface of the film.

[0082] As first substrate 1, a strontium titanate substrate, sapphire substrate, or silicon single-crystal substrate (Si substrate) can be used other than the MgO substrate. As materials of first main electrode layer 2, one of gold (Au), iridium (Ir), rhodium (Rh), ruthenium (Ru), silver (Ag), rhenium (Re) and palladium (Pd) and its conductive oxides can be used other than the Pt layer. Further, as the piezoelectric thin film, lead lanthanum zirconate titanate (PLZT), barium titanate, and other material can be used other than PZT.

[0083] To etch first piezoelectric thin film 3 into a predetermined shape, any of dry etching and wet etching can be used. Especially wet etching can be performed for a short period of time with simple equipment, and thus is advantageous to improvement of mass production. In wet-etching a PZT film, a mixed liquid of hydrofluoric acid and nitric acid, a mixed liquid of hydrofluoric acid, nitric acid, and acetic acid, or a liquid containing either liquid further diluted by pure water can be used. At this time, only first piezoelectric thin film 3 is etched, and thus control of the etching is easy. Therefore, etching of the side portions and variations in shape caused by etching can be reduced.

[0084]FIG. 5B shows first main electrode layer 2 is also etched to a predetermined shape. After first piezoelectric thin film 3 is etched, a photo-resist layer is applied to the surface of first substrate 1, exposed to light and developed using a predetermined photomask, and first main electrode layer 2 is etched using the resist pattern as a mask. Because first main electrode layer 2 is much thinner than first piezoelectric thin film 3, patterns can accurately be formed by any of dry etching and wet etching. Depending on the material of the electrode layer, dry etching or wet etching can be selected.

[0085] At this time, first main electrode layer 2 is patterned into the following shape. The overall shape is substantially the same as that of first piezoelectric thin film 3; however, the first main electrode layer is larger than the first piezoelectric thin film and the outer periphery is slightly exposed. In electrode leading area 108, a part of the first main electrode layer extends on the outer peripheral sides to form first main electrode layer projections 21 that project from first piezoelectric thin film 3. Such a pattern can easily be obtained by using a photomask.

[0086] When the overall shape of first main electrode layer 2 is extended from first piezoelectric thin film 3, first piezoelectric thin film 3 is not exposed to a chemical solution for etching first substrate 1 to remove it from thin film piezoelectric element 54. In general, the chemical solution for etching first substrate 1 for removal often etches first piezoelectric thin film 3 to some extent. When first main electrode layer 2 is formed wider than first piezoelectric thin film 3, first piezoelectric thin film 3 is protected by first main electrode layer 2 and is not brought into direct contact with the chemical solution. As a result, etching of first piezoelectric thin film 3 by the chemical solution is prevented.

[0087] When first substrate 1 is removed by grinding, or a chemical solution for etching does not etch first piezoelectric thin film 3, the above-described structure is unnecessary.

[0088]FIG. 5C shows a sectional view showing first opposite electrode layer 5 is further formed on first piezoelectric thin film 3. FIG. 5D is a plan view thereof. The shape of first opposite electrode layer 5 is substantially the same as that of first piezoelectric thin film 3. Additionally, first opposite electrode layer 5 is formed only on the surface layer of first piezoelectric thin film 3 not to be in electrical contact with first main electrode layer 2. In this embodiment, first opposite electrode layer 5 has a multi-layer structure. In other words, upper layer 52 is made of gold (Au) and lower layer 53 is a Pt layer like first main electrode layer 2. For lower layer 53, the same material as first main electrode layer 2 can be selected as required. Even with first opposite electrode layer 5 having such a multi-layer structure, a predetermined pattern can easily be formed by general techniques for the photolithography process and etching process.

[0089] As obvious from FIGS. 5C and 5D, in piezoelectric function area 106, first main electrode layer 2, first piezoelectric thin film 3, and first opposite electrode layer 5 are the same shape and are laminated like steps from the side of first substrate 1. On the other hand, in electrode leading area 108, as shown in the drawings, first electrode layer projections 21 where first main electrode layers 2 are partially exposed are formed. In these steps, formation and processing films on first substrate 1 are completed.

[0090] Next, formation and processing thin films on second substrate 11 are described with reference to FIGS. 6A through 6D.

[0091]FIG. 6A shows second main electrode layer 12 and second piezoelectric thin film 13 are laminated on second substrate 11 and then second piezoelectric thin film 13 is etched into a predetermined pattern shape.

[0092]FIG. 6B shows second main electrode layer 12 under this second piezoelectric thin film 13 is etched into a similar predetermined pattern shape. This second main electrode layer 12 is substantially the same as second piezoelectric thin film 13 in overall shape, but is slightly exposed from second piezoelectric thin film 13. This is the same as the pattern structure of first piezoelectric thin film 3 and first main electrode layer 2 on first substrate 1.

[0093]FIG. 6C shows second opposite electrode layer 15 is formed on second piezoelectric thin film 13. Second opposite electrode layer 15 is substantially the same second piezoelectric thin film 13 in overall shape, but is formed only on the surface of second piezoelectric thin film 13 not to be in electrical contact with second main electrode layer 12. This second opposite electrode layer 15 also has a multi-layer structure. Upper layer 151 is made of tin (Sn) and lower layer 152 is a Pt layer.

[0094] For second substrate 11, the same material as first substrate 1 can be used. Further, for second main electrode layer 12 and second piezoelectric thin film 13 formed on this second substrate 11, the materials of the films on first substrate 1 and methods forming them can be used.

[0095]FIG. 6D is a plan view showing the processed state as shown in FIG. 6C. Second main electrode layer 12, second piezoelectric thin film 13, and second opposite electrode layer 15 have the same pattern shape as a whole, but are laminated like steps from the side of second substrate 11. When seen from the front side, the piezoelectric element has second piezoelectric thin film 13 and second main electrode layer 12 each exposed in the outer periphery thereof. This structure prevents electrical contact between second main electrode layer 12 and second opposite electrode layer 15. Further, this structure also prevents second piezoelectric thin film 13 from being exposed to the chemical solution for etching second substrate 12 for removal.

[0096] On outer peripheral sides of electrode leading area 108, the pattern shape of second main electrode layer 12, second piezoelectric thin film 13, and second opposite electrode layer 15 are the same as that of first opposite electrode layer 5 and first piezoelectric thin film 3. However, on inner peripheral sides, second main electrode layer 12, second piezoelectric thin film 13, and second opposite electrode layer 15 are partially notched at corners. Therefore, in these areas, these layers are formed narrower than the first opposite electrode layer 5. When first substrate 1 and second substrate 11 are joined, first opposite electrode layer 5 in these notched areas is exposed to form first opposite electrode layer projections 51.

[0097] Next, a description is provided of a step in which first substrate 1 subjected to the steps shown in FIG. 5C and second substrate 11 subjected to the steps shown in FIG. 6C are joined to provide thin film piezoelectric element 54.

[0098]FIG. 7A is a sectional view showing first opposite electrode layer 5 and second opposite electrode layer 15 are brought into opposite intimate contact with and joined to each other. The two components are joined as follows. On the surface of first opposite electrode layer 5, an Au layer is formed as upper layer 52. On second opposite electrode layer 15, a Sn layer is formed as upper layer 151. When both upper layers are brought into intimate contact with each other and heated to temperatures at which Au-Sn eutectic reaction occurs, these two layers melt and join to form integrated adhesive layer 20.

[0099] Thus, a laminated structure via adhesive layer 20 can be obtained. Structures 50A and 50B forming element parts 54A and 54B, respectively, are produced so that a certain space is held therebetween. On first substrate 1 and second substrate 11, a plurality of such pairs of structures 50A and 50B are produced. However, for simplicity, only one pair is illustrated in the drawing.

[0100] In this embodiment, two components are joined by the Au-Sn eutectic reaction; however, the present invention is not limited to this method. Any combination of materials to be joined at relatively low temperatures can be used. For example, combinations arbitrarily selected from a first group consisting of Au, Ag, and Cu, and a second group consisting of Sn, Cd, and Au-containing Sn and Au-containing Cd can be used. Alternatively, soldering material can be formed on each upper layer for soldering. Further, conductive adhesive can also be used for joining.

[0101] When an MgO substrate is used as first substrate 1 and second substrate 11, a piezoelectric thin film formed on this MgO substrate is polarized in the direction perpendicular to the substrate surface. For this reason, such joining makes the direction of polarization opposite to each other. Therefore, when the same electric potential is applied to first main electrode layer 2 and second main electrode layer 12, and the same electric potential is applied to first opposite electrode layer 5 and second opposite electrode layer 15, first piezoelectric thin film 3 and second piezoelectric thin film 13 can perform the same expansion and contraction movements.

[0102] A pair of structures 50A and 50B is formed by the joining. A gap corresponding to the thickness of these structures 50A and 50B is generated between first substrate 1 and second substrate 11. By filling this gap with resin, insulating resin layer 6 is formed. FIG. 7B shows a gap is filled with insulating resin layer 6. The thickness of these structures 50A and 50B is approx. 10 μm. By adjusting the viscosity of the resin, the resin can be penetrated and filled into the gap. The resin that can be formed by the photolithography process and etching is used.

[0103] In this embodiment, a description is provided of a manufacturing method using an acrylic photosensitive resin. With acrylic photosensitive resin filled into the gap, the structures together with the substrates are placed on a hot plate, for example, heated at a temperature of 60° C. for 10 minutes, and successively heated at a temperature of 80° C. for 5 minutes. Such heat treatment pre-bakes the acrylic photosensitive resin, i.e. insulating resin layer 6. Pre-baking the insulating resin layer can protect structures 50A and 50B from the chemical solution for etching second substrate 11 for removal. Additionally, insulating resin layer 6 can be etched into a predetermined pattern shape easily.

[0104] After the resin filled into the gap between structures 50A and 50B are made pre-baked insulating resin layer 6, second substrate 11 is removed by etching. Because the outer periphery of structures 50A and 50B is completely protected by insulating resin layer 6, structures 50A and 50B are not directly exposed to etching solution except for second main electrode layer 12. For this reason, there is no phenomenon of deterioration of first piezoelectric thin film 3 and second piezoelectric thin film 13 caused by exposure to the etching solution. At this time, it is necessary to selectively remove second substrate 11 only. The methods of this selective removal include etching, grinding, and etching after grinding to a predetermined thickness. When first substrate 1 and second substrate 11 are made of the same material, the surface of first substrate 1 is covered with a resin that is not etched by the chemical solution, and then etching is performed. In this embodiment, a Pt layer is used as second main electrode layer 12. Thus, the second main electrode layer is not etched by the etching solution for second substrate 11 of MgO, i.e. a mixture of phosphoric acid and acetic acid.

[0105] When second substrate 11 is removed, structures 50A and 50B and the insulating resin layer 6 coupling the structures are exposed. In this state, insulating protective coat 18 for covering the surface of insulating resin layer 6 and second main electrode layer 12 is formed. Further, to partially expose second main electrode layer 12, holes 182 are provided through this insulating protective coat 18. This state is shown in FIG. 7C. These holes 182 can be formed when first openings 62 and second openings 64 are formed through insulting resin layer 6.

[0106] Next, as shown in FIG. 8A, insulating resin layer 6 is etched into a shape such that the insulating resin layer covers the outer periphery of structures 50A and 50B. Because piezoelectric thin films and other components are not exposed in this etching process, they are not etched. Thus, the etching process is stable and reproducibility is excellent. If insulating protective coat 18 formed on the surface is etched at the same time, etching is more efficient. Therefore, it is desirable that insulating protective coat 18 and insulating resin layer 6 are made of the same material. During this etching process, joint 70 for coupling two element parts 54A and 54B is formed at the same time.

[0107] Further, first openings 62 reaching first main electrode layer projections 2 and second openings 64 reaching first opposite electrode layer projections 51 are formed. In this etching process, after a photo-resist layer is formed on the surface of insulating protective coat 18, exposed to light and developed, insulating protective coat 18 and insulating resin layer 6 are etched at the same time. When insulating protective coat 18 and insulating resin layer 20 are made of the same photosensitive material, this process is easier. For example, when an acrylic photosensitive resin is used as insulating resin layer 6 and a similar acrylic photosensitive layer as insulating protective coat 18, insulating protective coat 18 and insulating resin layer 6 can be formed into a predetermined pattern shape at the same time only by exposure to light and development. The pattern shape after such a process is shown in FIG. 8A.

[0108] After such a process, pre-baked insulating resin layer 6 is further heated at high temperatures for final baking. When acrylic photosensitive resin is used as insulating resin layer 6, baking is completed by heating at a temperature of 150° C. for 30 minutes and successively heated at a temperature of 200° C. for 30 minutes.

[0109] Heating for pre-baking and heating for final baking in two stages facilitates etching of insulating resin layer 6 and removes solvent components remaining in insulating resin layer 6 without fail. Thus, bubbles generated by the solvent components can surely be eliminated.

[0110] Protecting the outer periphery of structures 50A and 50B by insulating resin layer 6 only can improve humidity resistance and prevent deterioration of piezoelectric characteristics.

[0111] Described in this embodiment is a case where acrylic photosensitive resin is used as insulating resin layer 6 and insulating protective coat 18. However, the present invention is not limited to this case. Such resins can include photosensitive epoxy resin, unsaturated polyester resin, thiol photosensitive resin, photolytic azide compound resin, naphtoquinone diazide (NQD) photosensitive resin, photo-crosslinkable dichromic acid resin, and polyvinyl photosensitive resin. The material is not limited to photosensitive resin. Any material on which a photo-resist layer can be formed and that is etched using the photo-resist layer as a mask can be used without restrictions.

[0112] Alternatively, after insulating resin layer 6 is formed into a predetermined pattern, insulating protective coat 18 can be applied and etched. In this case, insulating protective coat 18 can be photosensitive material or non-photosensitive material.

[0113] In the step shown in FIG. 8A, only insulting resin layer 6 and insulating protective coat 18 need to be etched when a predetermined pattern shape is formed or when openings are formed. Thus, accuracy of etching and yields are considerably improved. In other words, the step of forming first openings 62 reaching first main electrode layer projections 21 and second openings 64 reaching first opposite electrode layer projections 51 and the step of etching the outer periphery into a predetermined shape can be performed by etching insulating resin layer 6 and insulating protective coat 18 formed thereon only. For this reason, in comparison with a conventional method in which the first main electrode layer, first piezoelectric thin film, first opposite electrode layer, adhesive layer, second main electrode layer, second piezoelectric thin film and second opposite electrode layer are laminated and then a predetermined pattern is etched, short circuits and abnormal pattern shapes caused by remaining materials in etching can almost securely be prevented.

[0114] Next, to electrically connect second main electrodes 12 and first main electrode layer projections 21, first connection wirings 8 are formed via first openings 62. At the same time, second connection wirings 9 are formed to lead first opposite electrode layer projections 51 to the surface of insulating protective coat 18 via second openings 64. First connection wirings 8 and second connection wirings 9 are formed at the same time, and a predetermined pattern is formed by photolithography process and etching process at the same time. FIG. 8B shows first connection wirings 8 and second connection wirings 9 are formed in this manner.

[0115] In these processes, a shape of thin film piezoelectric element 54 is completed although it is still joined onto first substrate 1. Thereafter, thin film piezoelectric element 54 is removed from first substrate 1 by etching. For this purpose, after resin, e.g. wax, is applied to the surface of thin film piezoelectric element 54, first substrate 1 is removed by etching. At this time, resin, e.g. wax, which is not etched by the chemical solution for etching first substrate 1 is used.

[0116] After first substrate 1 is removed by etching and then resin, e.g. wax, is removed by melting, thin film piezoelectric element 54 completely separated from each substrate can be obtained. Such-element is shown in FIG. 8C.

[0117] In the method of manufacturing a thin film piezoelectric element of this embodiment, first piezoelectric thin film 3 and second piezoelectric thin film 13 are etched on first substrate 1 and second substrate 11, respectively. Thus, etching after lamination is performed only on resin layer made of insulating resin layer 6 and insulating protective coat 18. In the conventional method of etching piezoelectric thin films in a laminated state, material remaining on side walls of the piezoelectric thin films may cause short circuits between upper and lower electrode layers or reduction in the width of the pattern. However, in the manufacturing method of this embodiment, respective components are etched separately, and only the resin layer is etched after lamination. Thus, such failures can securely be prevented and yields can considerably be improved.

[0118] This thin film piezoelectric element 54 is bonded to flexure 460, i.e. a supporting member, by an adhesive resin layer. Connection electrode pads provided on first connection wirings 8 and second connection wirings 9 are connected to electrode pads for piezoelectric element 464 provided on flexure 460 via wire leads 467. Thus, actuator 905 is completed.

[0119] Joining first substrate 1 and second substrate 11 is not limited to the above-mentioned eutectic reaction. A conductive adhesive can be applied to the opposed surfaces of first opposite electrode layer 5 and second opposite electrode layer 15 to join them together. At this time, the conductive adhesive can be applied to both opposite electrode layers or one of the opposite electrode layers. When the conductive adhesive is applied to first opposite electrode layer projection 51, and second opening 64 is formed by etching insulating resin layer 6, either adhesive layer 20 made of the conductive adhesive or first opposite electrode layer 5 can be exposed. The conductive adhesive is not necessarily required in the piezoelectric function area. In other words, the conductive adhesive is used in the electrode leading area, and an insulating material can be used for bonding in the piezoelectric function area.

[0120] When the adhesive layer is formed by eutectic reaction, the opposite electrode layers melt once. Thus, self-alignment is possible. For this reason, even if first opposite electrode layer 5 is aligned with second opposite electrode layer 15 with low accuracy, the self-alignment effect at melting can align both layers with high accuracy for bonding.

[0121] Additionally, in this embodiment, insulating resin layer 6 filled is heat-treated under the conditions for pre-baking, before removal of the second substrate. After the removal of second substrate 11, insulating resin layer 6 is etched into a predetermined pattern shape and then final baking is performed. Therefore, insulating resin layer 6 is accurately patterned, and bubbles likely to occur in insulating resin layer 6 can securely be inhibited.

Second Exemplary Embodiment

[0122]FIG. 9 is a plan view of thin film piezoelectric element 540 in accordance with the second exemplary embodiment of the present invention. FIG. 10 is a sectional view thereof taken along line 228-228 of FIG. 9. Thin film piezoelectric element 540 of this embodiment also has a pair structure. The structure of piezoelectric function area 226 of respective element parts 540A and 540B is the same as that of thin film piezoelectric element 54 of the first exemplary embodiment.

[0123] Piezoelectric function area 226 of respective element parts 540A and 540B are structured so that first piezoelectric thin film 203 sandwiched between first main electrode layer 202 and first opposite electrode layer 205 and second piezoelectric thin film 213 sandwiched between second main electrode layer 212 and second opposite electrode layer 215 are coupled with first opposite electrode layer 205 and second opposite electrode layer 215 physically and electrically connected to each other via conductive adhesive layer 232. The outer periphery of the element is protected by insulating layer 222 of the same thickness. On this insulating layer 222 and second main electrode layer 212, insulating protective coat 220 is formed.

[0124] In thin film piezoelectric element 540 of this embodiment, the structure of electrode leading area 224 is different from that of thin film piezoelectric element 54 of the first embodiment. The difference is mainly described hereinafter. Also in this embodiment, because this insulating layer 222 is made of resin material, it is hereinafter referred to as insulating resin layer 222.

[0125] On each of the outer peripheral sides of electrode leading area 224, first main electrode layer projections 2021 and second main electrode layers 212 are connected by first connection wirings 218 via first openings 262 through insulating resin layer 222. On the other hand, on the inner peripheral sides, element parts 540A and 540B are coupled by first piezoelectric thin films 203 and first opposite electrode layers 205 thereof to form joint 230. Two element parts 540A and 540B are coupled by this joint 230 to form an integrated structure. First opposite electrode layers 205 of respective element parts 540A and 540B are coupled to each other. As a result, first opposite electrode layers 205 and second opposite electrode layers 215 of respective element parts are all electrically connected. Insulating resin layer 222 in joint 230 also has second opening 260 formed therethrough. Via this second opening 260, first opposite electrode layer 205 is connected and lead to the surface by second connection wiring 219.

[0126] As described above, for thin film piezoelectric element 540 of this embodiment, the number of the connection electrode pads for connection to the electrode pads for piezoelectric element on the flexure is three. The three connection electrode pads are provided on the first connection wirings and second connection wiring.

[0127] Also in this embodiment, an Au layer is formed as upper layer 2052 on the surface of first opposite electrode layer 205. A Sn layer is formed as upper layer 2151 on second opposite electrode layer 215. Upper layers 2052 and 2151 are brought into intimate contact with each other, and heated to temperatures at which Au-Sn eutectic reaction occurs to melt and form adhesive layer 232.

[0128] Hereinafter, a description is mainly provided of the steps different from those of the first embodiment, in a method of manufacturing thin film piezoelectric element 540 of this second embodiment. FIGS. 11A through 13C are drawings for illustrating the major steps, in a method of manufacturing thin film piezoelectric element 540 of this embodiment. Also in thin film piezoelectric element 540 of this embodiment, the steps are described with reference to a sectional shape taken along line 228-228 of FIG. 9.

[0129] First, formation and processing thin films on first substrate 201 is described using FIGS. 11A through 11C.

[0130]FIG. 11A shows first main electrode layer 202 and then first piezoelectric thin film 203 are formed into predetermined patterns on first substrate 201. For example, first, when an electrode layer to be first main electrode layer 202 is formed, the layer is patterned using a metal mask at the same time. Alternatively, after an electrode layer to be first main electrode layer 202 is formed, a pattern is formed by a photolithography process and etching process. Also in this embodiment, first main electrode layer projections 2021 are formed.

[0131] Then, after a piezoelectric thin film to be first piezoelectric thin film 203 is laminated, this piezoelectric thin film is etched into a predetermined shape. In electrode leading area 224, the pattern shape of first piezoelectric thin film 203 is partly different from that of thin film piezoelectric element 54 of the first embodiment. In other words, in electrode leading area 224, joint 230 for coupling first piezoelectric thin films 203 of both sides is formed.

[0132] Because the materials of first substrate 201, first main electrode 202, and first piezoelectric thin film 203 and conditions for forming and etching them are the same as those of the first embodiment, the descriptions thereof are omitted.

[0133]FIG. 11B is a sectional view showing first opposite electrode layer 205 is further formed on first piezoelectric thin film 203. FIG. 11C is a plan view thereof. First opposite electrode layer 205 has substantially the same shape as first piezoelectric thin film 203. Additionally, first opposite electrode layer 205 is formed only on the surface of first piezoelectric thin film 203 not to be in electrical contact with first main electrode layer 202. In this embodiment, first opposite electrode layer 205 is also formed on first piezoelectric thin film 203 in joint 230.

[0134] Further, also in this embodiment, first opposite electrode layer 205 has a multi-layer structure. Upper layer 2052 is made of gold (Au), and a Pt layer is used as lower layer 2053 like first main electrode layer 202. For lower layer 2053, the same material as first main electrode layer 202 can be selected as required. Even with first opposite electrode layer 205 having such a multi-layer structure, a predetermined pattern can easily be formed by general techniques for the photolithography process and etching process.

[0135] As obvious from FIGS. 11B and 11C, in piezoelectric function area 226, first main electrode layer 202, first piezoelectric thin film 203, and first opposite electrode layer 205 have the same shape and laminated like steps from the side of first substrate 201. On the other hand, in electrode leading area 224, as shown in the drawing, first electrode layer projections 2021 where first main electrode layer 202 is partially exposed are provided. In joint 230, first main electrode layer 202 is etched out to electrically separate right and left sides. In these steps, formation and processing films on first substrate 201 is completed.

[0136] Next, formation and processing thin films on second substrate 211 is described with reference to FIGS. 12A and 12B.

[0137]FIG. 12A is a sectional view showing second main electrode layer 212, second piezoelectric thin film 213 and second opposite electrode layer 215 are formed on second substrate 211. FIG. 12B is a plan view thereof.

[0138] These pattern shapes on second substrate 211 are the same as those on first substrate 201 except for electrode leading area 224. On each of outer peripheral sides of electrode leading area 224, the pattern shape of second main electrode layer 212, second piezoelectric thin film 213, and second opposite electrode layer 215 are the same as that of first opposite electrode layer 205 and first piezoelectric thin film 203. However, on inner peripheral sides, second main electrode layer 212, second piezoelectric thin film 213, and second opposite electrode layer 215 are partially notched at corners. Therefore, in these areas, these layers are formed narrower than first opposite electrode layer 205. When first substrate 201 and second substrate 211 are joined, first opposite electrode layer 205 in these notched areas is exposed to from first opposite electrode layer projections 2051. This shape is the same as that of the first embodiment. As shown in the drawing, no joint is provided on this second substrate 211. Also, second opposite electrode layer 215 has a multi-layer structure. Upper layer 2151 is made of stannum (St) and a Pt layer is used as lower layer 2152.

[0139] For second substrate 211, the same material as first substrate 201 can be used. Further, for second main electrode layer 212 and second piezoelectric thin film 213 formed on this second substrate 211, the same materials of the films on first substrate 201 and method of forming them can be used. These descriptions are omitted because they are the same as the first embodiment.

[0140] Next, a description is provided of a step in which first substrate 201 and second substrate 211 are joined to provide thin film piezoelectric element 540 with reference to FIG. 13A through 13C.

[0141]FIG. 13A shows first opposite electrode layer 205 and second opposite electrode layer 215 are opposed and joined to each other, then second substrate 211 is removed by etching, and insulating protective coat 220 is further formed. Through this insulating protective coat 220, holes 240 are provided in predetermined positions on second main electrode layer 212. Because the process of forming these shapes is the same as the first embodiment, descriptions are omitted.

[0142] In this embodiment, on joint 230 and first opposite electrode layer projection 2051, insulating resin layer 222 and insulating protective coat 220 are also formed. Formation of insulating resin layer 222 and insulating protective coat 222 in this manner further increases the strength of joint 203. As a result, when thin film piezoelectric element 540 of a pair structure is bonded onto a supporting member, breakage of the element is unlikely to occur.

[0143]FIG. 13B shows first connection wirings 218 and second connection wiring 219 are formed through the element. In other words, each first connection wiring 218 electrically connects first main electrode layer projection 2021 and second main electrode layer 212 via first opening 262 through insulating resin layer 222, and also has an electrode pad for external connection. Similarly, second connection wiring 219 connects to first opposite electrode layer projection 2051 via second opening 260 through insulating resin layer 222 and insulating protective coat 220, leads the projection to the surface, and forms a connection electrode pad. First connection wirings 218 and second connection wiring 219 are made by forming a metal thin film by sputtering or evaporation and then patterning the film by a photolithography process and etching process.

[0144] In these steps, a shape of thin film piezoelectric element 540 is completed although it is still joined onto first substrate 201. Thereafter etching out first substrate 201 can provide thin film piezoelectric element 540 completely separated from the substrate as shown in FIGS. 9 and 10.

[0145] In the method of manufacturing thin film piezoelectric element 540 of this embodiment, first piezoelectric thin film 203 is etched on first substrate 201 and second piezoelectric thin film 213 is etched on second substrate 211 separately. Thus, etching after lamination is performed only on the resin layer made of insulating resin layer 222 and insulating protective coat 220. In the conventional method of etching piezoelectric thin films in a laminated state, material remaining on side walls of the piezoelectric thin film may cause short circuits between upper and lower electrode layers or reduction in the width of the pattern. However, in the manufacturing method of this embodiment, respective components are etched separately, and only the resin layer is etched after lamination. Thus, such failures can securely be prevented and yields can considerably be improved.

[0146] This thin film piezoelectric thin film 540 can be driven using three terminals. When the connection electrode pad provided on second connection wiring 219 is grounded, a voltage is applied to one of the connection electrode pads provided on first connection wirings 218 and the same voltage of reversed polarity to the other of the connection pads, the operation shown in FIG. 2 can be performed. This simplifies the terminal structure, thus realizing a thin film piezoelectric element having excellent characteristics and a method of manufacturing the element with high yields.

[0147]FIG. 14 is a sectional view of thin film piezoelectric element 550 in accordance with a modification of this embodiment. Thin film piezoelectric element 550 of this modification is different from thin film piezoelectric element 540 in that no opening open to first opposite electrode layer projection 2051 is provided through insulating resin layer 222 and insulating protective coat 220. For a thin film piezoelectric element having a pair structure, not only one having a three-terminal structure but also one having a structure of this modification works. Thin film piezoelectric element 550 of this modification has two terminals. However, when voltages of reversed polarity are applied to the terminals without the opposite electrode side grounded, the opposite electrode side is substantially at zero potential and the element performs similar operation.

[0148] The method of manufacturing this thin film piezoelectric element 550 is the same as thin film piezoelectric element 540, except that second opening 260 and second connection wiring 219 are not formed.

Third Exemplary Embodiment

[0149]FIG. 15 is a sectional view of an electrode leading area of thin film piezoelectric element 560 in accordance with the third exemplary embodiment of the present invention. Thin film piezoelectric element 560 of this embodiment also has a pair structure. The structure of a piezoelectric function area of each of element parts 560A and 560B is the same as that of thin film piezoelectric element 540 of the second exemplary embodiment.

[0150] In other words, the piezoelectric function area of each of element parts 560A and 560B is structure so that first piezoelectric thin film 303 sandwiched between first main electrode layer 302 and first opposite electrode layer 305 and second piezoelectric thin film 313 sandwiched between second main electrode layer 312 and second opposite electrode layer 315 are coupled with first opposite electrode layer 305 and second opposite electrode layer 315 physically and electrically connected to each other via conductive adhesive layer 332. The outer periphery of the element is protected by insulating layer 322 of the same thickness. On this insulating layer 322 and second main electrode layer 312, insulating protective coat 320 is formed. Also in this embodiment, because insulating layer 322 is made of resin material, it is hereinafter referred to as insulating resin layer 322.

[0151] In thin film piezoelectric element 560 of this embodiment, the structure of an electrode leading area is different from that of thin film piezoelectric element 540 of the second embodiment. The difference is mainly described hereinafter.

[0152] In the electrode leading area, first main electrode layer 302, first piezoelectric thin film 303, second main electrode layer 312, and second piezoelectric thin film 313 are coupled to form joint 330. The gap in joint 330 defined by first opposite electrode layer 305, conductive adhesive layer 332, and second opposite electrode layer 315 is filled with insulating resin layer 322.

[0153] This joint 330 couples two element parts 560A and 560B into an integrated structure. Additionally, first main electrode layers 302 and second main electrode layers 312 of respective element parts 560A and 560B are coupled with each other. As a result, first main electrode layers 302 are electrically connected with each other and second main electrode layers 312 are electrically connected with each other.

[0154] Further, connection wiring 318 is formed from first opposite layer projection 3051 extending from first opposite electrode 305 of each of element parts 560A and 560B, via second opening 360 through insulating resin layer 322 and insulating protective coat 320. On these connection wirings 318, connection electrode pads are provided.

[0155] As described above, for thin film piezoelectric element 560 of this embodiment, only connection electrode pads from connection wirings 318 are connected to the electrode pads for piezoelectric element on the flexure. The total number of connection electrode pads is only two, one from each of element parts 560A and 560B.

[0156] Also in this embodiment, an Au layer is formed as upper layer 3052 on the surface of first opposite electrode layer 305 and a Sn layer is formed as upper layer 3151 on second opposite electrode layer 315. Upper layers 3052 and 3151 are brought into intimate contact with each other, heated to temperatures at which Au-Sn eutectic reaction occurs to melt and form adhesive layer 332.

[0157] Hereinafter, a description is provided of a method of manufacturing thin film piezoelectric element 560 of this embodiment. Also in this embodiment, the descriptions are provided with reference to sectional shape of the electrode leading area.

[0158]FIG. 16A is a sectional view showing first main electrode layer 302, first piezoelectric thin film 303, and first opposite electrode layer 305 are laminated on first substrate 301 and predetermined patterns are formed. FIG. 16B is a plan view thereof.

[0159] As obvious from FIG. 16B, in the piezoelectric function area, first main electrode layer 302, first piezoelectric thin film 303 and first opposite electrode layer 305 are analogous and structured to be laminated like steps from the side of first substrate 301. This shape is the same as that of the first and second embodiments.

[0160] In the electrode leading area, first main electrode layer 302 and first piezoelectric thin film 303 are also formed in joint 330. This joint couples the patterns on both sides. First opposite electrode layer 305 is formed only on the surface of first piezoelectric thin film 303 other than joint 330.

[0161] Further, also in this embodiment, first opposite electrode layer 305 has a multi-layer structure. Upper layer 3052 is made of gold (Au), and a Pt layer is used as lower layer 3053 like first main electrode layer 302. For lower layer 3053, the same material as first main electrode layer 302 can be selected as required. Even with first opposite electrode layer 305 having such a multi-layer structure, a predetermined pattern can easily be formed by general techniques for the photolithography process and etching process.

[0162]FIG. 17A is a sectional view showing second main electrode layer 312, second piezoelectric thin film 313, and second opposite electrode layer 315 are formed on second substrate 311. FIG. 17B is a plan view thereof.

[0163] These patterns on second substrate 311 are the same as the patterns on first substrate 301 except for the electrode leading area. In joint 330 in the electrode leading area, second main electrode layer 312 and second piezoelectric thin film 313 are formed to couple the patterns on both sides. On each of the outer peripheral sides in the electrode leading area, second main electrode layer 312, second piezoelectric thin film 313 and second opposite electrode layer 315 are partially notched to be narrower than first opposite electrode layer 305. For this reason, as shown in FIG. 15, when first opposite electrode layer 305 and second opposite electrode layer 315 are joined, first opposite electrode layer 305 in these notched areas are exposed to form first opposite electrode layer projections 3051. In contrast, on each of the inner peripheral sides, the shape of the layers on the second substrate corresponds to the shape of the layers on first substrate 301.

[0164] Second opposite electrode layer 315 also has a multi-layer structure. Upper layer 3151 is made of tin (Sn) and a Pt layer is used as lower layer 3152.

[0165] For second substrate 311, the same material as first substrate 301 can be used. Further, for second main electrode layer 312 and second piezoelectric thin film 313 formed on this second substrate 311, the same materials of the films on first substrate 301 and method of forming them can be used. These descriptions are omitted because they are the same as the first embodiment.

[0166]FIG. 18A is a sectional view showing first opposite electrode layer 305 and second opposite electrode layer 315 are opposed and joined to each other, then second substrate 311 is etched out, and insulating protective coat 320 is formed on the exposed surface.

[0167] As obvious from the drawing, insulating resin layer 322 is also formed in the gap in joint 330 sandwiched between first piezoelectric thin film 303 and second piezoelectric thin film 313. Additionally, insulating resin layer 322 is formed to cover the outer periphery including first opposite electrode layer projections 3051 provided on the outer peripheral sides.

[0168] Because insulating resin layer 322, first main electrode layer 302, first piezoelectric thin film 303, second piezoelectric thin film 313 and second main electrode layer 312 are formed in joint 330 in this manner, the strength of joint 330 is further increased. This structure can prevent breakage of thin film piezoelectric element 560 of a pair structure during handling.

[0169]FIG. 18B is a sectional view showing insulating protective coat 320 and insulating resin layer 322 are etched. Like the first and second embodiments, the pattern of this etching is wider than first main electrode layer 302. Second openings 360 are also formed through insulating resin layer 322 on first opposite electrode layer projections 3051. These steps can be performed by etching the resin layer made of insulating protective coat 320 and insulating resin layer 322. Thus, the processing can easily be performed with high accuracy.

[0170] Thereafter, connection wirings 318 each for connecting to first opposite electrode layer projection 3051 are formed via second openings 360. In these steps, a shape of thin film piezoelectric element 560 is completed although it is still joined onto first substrate 301. Thereafter etching out first substrate 301 can provide thin film piezoelectric element 560 completely separated from the substrate as shown in FIG. 15.

[0171] In the method of manufacturing thin film piezoelectric element 560 of this embodiment, first piezoelectric thin film 303 is etched on first substrate 301 and second piezoelectric thin film 313 is etched on second substrate 311 separately. Thus, etching after lamination is performed only on the resin layer made of insulating resin layer 322 and insulating protective coat 320. In the conventional method of etching piezoelectric thin films in a laminated state, material remaining on side walls of the piezoelectric thin film may cause short circuits between upper and lower electrode layers or reduction in the width of the pattern. However, in the manufacturing method of this embodiment, respective components are etched separately, and only the resin layer is etched after lamination. Thus, such failures can securely be prevented and yields can considerably be improved.

[0172] This thin film piezoelectric thin film 560 can be driven using two terminals. When voltages of reversed polarity are applied to the connection electrode pads provided on connection wirings 318, the operation shown in FIG. 2 can be performed. When such voltages are applied, the opposite electrode side is substantially at zero potential and the element performs expansion and contraction movements even without being grounded.

[0173] The method of manufacturing thin film piezoelectric element 560 simplifies the patterning process and the structure of terminals, thus providing excellent characteristics and improving yields.

[0174] In this embodiment, insulating resin layer 322 is also formed in the gap in joint 330 sandwiched between first piezoelectric thin film 303 and second piezoelectric thin film 313. However, first opposite electrode layer 305 and second opposite electrode layer 315 can be formed and joined and adhesive layer 332 can be provided in this region.

[0175] In the first through third exemplary embodiments, descriptions are provided of a thin film piezoelectric element having a pair structure. However, the present invention is not limited to this structure. Only one element part of the thin film piezoelectric element described in the first embodiment can be used as a thin film piezoelectric element.

[0176] Further, the opening formed in an insulating layer is not limited to a via-hole. Unless the connection wiring is in contact with the piezoelectric thin films, opposite electrode layers, or other components, no restrictions are imposed on the shape of the opening.

[0177] In the first through third exemplary embodiments, as a thin film piezoelectric element having a pair structure and symmetrical mirror images, each element part is pentagonal. The present invention is not limited to this shape. For example, a rectangular shape or triangular shape can be used.

[0178] In the first through third exemplary embodiments, the first opposite electrode layer and second opposite electrode layer are joined using a conductive adhesive layer. The first and second opposite electrode layers can be joined by ultrasonic bonding or heat welding, for example. Alternatively, a conductive adhesive can be used. Additionally, physical and electrical connection therebetween need not be provided on the entire surface. 

What is claimed is:
 1. A thin film piezoelectric element comprising: a structure in which a first piezoelectric thin film sandwiched between a first main electrode layer and a first opposite electrode layer and a second piezoelectric thin film sandwiched between a second main electrode layer and a second opposite electrode layer are coupled so that the first opposite electrode layer and the second opposite electrode layer are opposed and physically and electrically connected to each other; and an insulating layer covering an outer periphery along a thickness of the structure; wherein the first main electrode layer has a first main electrode layer projection partially extending from the first piezoelectric thin film, a first opening is formed through the insulating layer on the first main electrode layer projection, and a first connection wiring for connecting the first main electrode layer projection and the second main electrode layer is disposed via the first opening.
 2. The thin film piezoelectric element of claim 1, wherein the first connection wiring is disposed on a front surface of the second main electrode layer.
 3. A thin film piezoelectric element comprising: a structure in which a first piezoelectric thin film sandwiched between a first main electrode layer and a first opposite electrode layer and a second piezoelectric thin film sandwiched between a second main electrode layer and a second opposite electrode layer are coupled so that the first opposite electrode layer and the second opposite electrode layer are opposed and physically and electrically connected to each other; and an insulating layer covering an outer periphery along a thickness of the structure; wherein the first main electrode layer in an electrode leading area has a first main electrode layer projection partially extending from the first piezoelectric thin film, a first connection wiring for connecting the first main electrode layer projection and the second main electrode layer is disposed via a first opening formed through the insulating layer on the first main electrode layer projection; and the second main electrode layer, the second piezoelectric thin film, and the second opposite electrode layer in the electrode leading area are formed narrower than the first opposite electrode layer to provide an region in which the insulating layer is provided on the first opposite electrode layer, and a second connection wiring for electrical connection to the first opposite electrode layer is disposed via a second opening formed through the insulating layer on the first opposite electrode layer in this region.
 4. The thin film piezoelectric element of claim 3, wherein the first connection wiring and the second connection wiring are structured to extend to the same front surface of the second main electrode of the structure.
 5. The thin film piezoelectric element of claim 1, wherein the first opposite electrode layer and the second opposite electrode layer are structured to be physically and electrically connected by a conductive adhesive layer.
 6. The thin film piezoelectric element of claim 3, wherein the first opposite electrode layer and the second opposite electrode layer are structured to be physically and electrically connected by a conductive adhesive layer.
 7. A thin film piezoelectric element comprising: a pair of element parts disposed in a plane with a predetermined space held therebetween, a piezoelectric function area working as a piezoelectric body of the pair of element parts having mirror images symmetrical with respect to a centerline of the predetermined space; a joint for coupling the element parts in a part of the predetermined space using at least one kind of material comprising the element parts; and each of the pair of element parts comprising: a structure in which a first piezoelectric thin film sandwiched between a first main electrode layer and a first opposite electrode layer and a second piezoelectric thin film sandwiched between a second main electrode layer and a second opposite electrode layer are coupled so that the first opposite electrode layer and the second opposite electrode layer are opposed and physically and electrically connected to each other; an insulating layer covering an outer periphery along a thickness of the structure; wherein the first main electrode layer in an electrode leading area has a first main electrode layer projection partially extending from the first piezoelectric thin film, the second main electrode layer, the second piezoelectric thin film, and the second opposite electrode layer in the electrode leading area are formed narrower than the first opposite electrode layer to provide an region in which the insulating layer is provided on the first opposite electrode layer, and at least one of a first opening formed through the insulating layer on the first main electrode layer projection or a second opening formed through the insulating layer on the first opposite electrode layer in this region is provided; and a connection wiring connecting to one of the first opposite electrode layer and the first main electrode layer and leading to a surface layer via one of the first opening and the second opening.
 8. The thin film piezoelectric element of claim 7, wherein the first opposite electrode layer and the second opposite electrode layer are structured to be physically and electrically connected by a conductive adhesive layer.
 9. The thin film piezoelectric element of claim 7, wherein the joint is formed of the insulating layer; the structure has the first opening and the second opening formed therein; and the connection wiring comprises: a first connection wiring for connecting the first main electrode layer projection and the second main electrode layer via the first opening; and a second connection wiring for connecting to the first opposite electrode layer and leading to the surface layer via the second opening.
 10. The thin film piezoelectric element of claim 7, wherein the joint is formed of at least the first opposite electrode layer and the first piezoelectric thin film; the structure has the first opening, and the second opening common to the element parts; and the connection wiring comprises: a first connection wiring for connecting the first main electrode layer projection and the second main electrode layer via the first opening; and a second connection wiring for connecting to the first opposite electrode layer and leading to the surface layer via the second opening.
 11. The thin film piezoelectric element of claim 7, wherein the joint is formed of at least the first opposite electrode layer and the first piezoelectric thin film; the structure has the first opening formed through the insulating layer on the first main electrode layer projection; and the connection wiring connects the first main electrode layer projection and the second main electrode layer via the first opening.
 12. The thin film piezoelectric element of claim 7, wherein the joint is formed of the first main electrode layer, the first piezoelectric thin film, the second main electrode layer, and the second piezoelectric thin film; the structure has the second opening formed through the insulating layer on the first opposite electrode layer projection; and the connection wiring for connecting to the first opposite electrode layer projection and leading to the surface layer is formed via the second opening.
 13. The thin film piezoelectric element of one of claims 5, 6, and 8, wherein each of the first opposite electrode layer and the second opposite electrode layer is made of at least two layers, a combination of materials of upper layers of the first opposite electrode and the second opposite electrode is arbitrarily selected from a first group consisting of gold (Au), silver (Ag), and cupper (Cu) and a second group consisting of tin (Sn), cadmium (Cd), Au-containing Sn alloys, and Au-containing Cd alloys, and the conductive adhesive layer is made by alloying the upper layers with each other.
 14. The thin film piezoelectric element of one of claims 5, 6, and 8, wherein each of the first opposite electrode layer and the second opposite electrode layer is made of at least two layers, each upper layer is made of solder, or one upper layer is made of solder and the other upper layer is made of at least one material of the solder, and the conductive adhesive layer is made by melting the upper layers into one.
 15. The thin film piezoelectric element of one of claims 5, 6, and 8, wherein the conductive adhesive layer is made of an adhesive comprising one of resin paste and conductive polymer including a conductive particle and an adhesive binder.
 16. An actuator comprising: a supporting member; and a pair of thin film piezoelectric elements disposed on the supporting member, expanding and contracting in directions opposite to each other, and structured as defined in claim
 7. 17. A disk drive comprising: a disk-shaped record medium; a head for performing at least one of recording and reproducing operations on the record medium; and a first positioning means and a second positioning means for positioning the head in a specific position on the record medium; wherein the first positioning means is a driving means for rotating an arm, and the arm holds a supporting member having the head mounted thereon; and the second positioning means is an actuator comprising the supporting member and a pair of thin film piezoelectric elements attached to the supporting member, and the actuator is structured as defined in claim
 16. 18. A method of manufacturing a thin film piezoelectric element comprising the steps of: laminating a first main electrode layer, a first piezoelectric thin film, and a first opposite electrode layer on a first substrate in this order; in a piezoelectric function area in which the element works as a piezoelectric body, forming the first main electrode layer, the first piezoelectric thin film, and the first opposite electrode layer into the same shape, and in an electrode leading area, forming the first main electrode layer, the first piezoelectric thin film, and the first opposite electrode layer into a shape such that the first main electrode layer is partially extended and exposed from the first piezoelectric thin film to form a first main electrode layer projection; laminating a second main electrode layer, a second piezoelectric thin film, and a second opposite electrode layer on a second substrate in this order; in the piezoelectric function area, forming these layers into the same shape as the first main electrode layer, the first piezoelectric thin film, and the first opposite electrode layer formed on the first substrate, and in a part of the electrode leading area, forming the second main electrode layer, the second piezoelectric thin film, and the second opposite electrode layer into a shape such that the second main electrode layer, the second piezoelectric thin film, and the second opposite electrode layer are notched; opposing and joining the first opposite electrode layer and the second opposite electrode layer to each other using a conductive adhesive layer to form an integrated structure; forming an insulating layer for filling a gap in the structure sandwiched between the first substrate and the second substrate; removing the second substrate; forming the exposed insulating layer into a shape such that the insulating layer covers at least an outer periphery of the first main electrode layer; forming a first opening reaching the first main electrode layer projection through the insulating layer on the first main electrode layer projection, and forming a second opening reaching one of the first opposite electrode layer projection and the adhesive layer through the insulating layer on the first opposite electrode layer projection; and forming a first connection wiring for connecting the first main electrode layer projection and the second main electrode via the first opening, and a second connection wiring for leading from one of the first opposite electrode layer projection and the adhesive layer to a front surface of the insulating layer via the second opening.
 19. A method of manufacturing a thin film piezoelectric element comprising the steps of: laminating a first main electrode layer, a first piezoelectric thin film, and a first opposite electrode layer on a first substrate in this order; in a piezoelectric function area of a pair of symmetrical shapes with respect to a centerline of a predetermined space in which the element works as a piezoelectric body, forming the first main electrode layer, the first piezoelectric thin film, and the first opposite electrode layer into the same shape, and in an electrode leading area, forming the first main electrode layer into a shape such that the first main electrode layer is partially extended and exposed from the first piezoelectric thin film to provide a first main electrode layer projection; laminating a second main electrode layer, a second piezoelectric thin film, and a second opposite electrode layer on a second substrate in this order; forming these layers into a shape same as the pair of shapes formed on the first substrate, and in a part of the electrode leading area, forming these layers into a shape such that the second main electrode layer, the second piezoelectric thin film, and the second opposite electrode layer are notched; opposing and joining the first opposite electrode layer and the second opposite electrode layer to each other using a conductive adhesive layer to form an integrated pair structure; forming an insulating layer for filling a gap in the structure sandwiched between the first substrate and the second substrate; removing the second substrate; forming the insulating layer into a shape such that the insulating layer covers at least an outer periphery of the first main electrode layer and couples a pair structure in a part of the predetermined space; forming a first opening reaching the first main electrode layer projection through the insulating layer on the first main electrode layer projection, and forming a second opening reaching one of the first opposite electrode layer projection and the adhesive layer through the insulating layer on the first opposite electrode layer projection; and forming a first connection wiring for connecting the first main electrode layer projection and the second main electrode layer via the first opening, and a second connection wiring for leading from one of the first opposite electrode layer projection and the adhesive layer to a front surface of the insulating layer via the second opening.
 20. A method of manufacturing a thin film piezoelectric element comprising the steps of: laminating a first main electrode layer, a first piezoelectric thin film, and a first opposite electrode layer on a first substrate in this order; in a piezoelectric function area of a pair of symmetrical shapes with respect to a centerline of a predetermined space in which the element works as a piezoelectric body, forming the first main electrode layer, the first piezoelectric thin film, and the first opposite electrode layer into the same shape, and in an electrode leading area, partially extending and exposing the first main electrode layer from the first piezoelectric thin film to provide a first main electrode layer projection, and forming a shape in which the pair of shapes are coupled by the first main electrode layer projection, the first piezoelectric thin film, and the first opposite electrode layer; laminating a second main electrode layer, a second piezoelectric thin film, and a second opposite electrode layer on a second substrate in this order; in the piezoelectric function area, forming these layers into a shape same as the pair of shapes formed on the first substrate, and in the electrode leading area, forming these layers into a shape such that the second main electrode layer, the second piezoelectric thin film, and the second opposite electrode layer are partially notched in the same position; opposing and joining the first opposite electrode layer and the second opposite electrode layer to each other using a conductive adhesive layer to form an integrated pair structure; forming an insulating layer for filling a gap in the structure sandwiched between the first substrate and the second substrate; removing the second substrate; forming the insulating layer into a shape such that the insulating layer covers at least an outer periphery of the first main electrode layer; forming a first opening through the insulating layer on the first main electrode layer projection; and forming a first connection wiring for connecting the first main electrode layer projection and the second main electrode layer via the first opening.
 21. The thin film piezoelectric element of claim 20, further comprising the steps of: forming a second opening through the insulating layer on the first opposite electrode layer projection exposed by notching the second main electrode layer, the second piezoelectric thin film and the second opposite electrode layer; and forming a second connection wiring for connecting to the first opposite electrode layer projection and leading to a surface layer via the second opening.
 22. A method of manufacturing a thin film piezoelectric element comprising the steps of: laminating a first main electrode layer, a first piezoelectric thin film, and a first opposite electrode layer on a first substrate in this order; in a piezoelectric function area of a pair of symmetrical shapes with respect to a centerline of a predetermined space in which the element works as a piezoelectric body, forming the first main electrode layer, the first piezoelectric thin film, and the first opposite electrode layer into the same shape, and in an electrode leading area, forming a shape in which the pair of shapes are coupled by the first main electrode layer, and the first piezoelectric thin film; laminating a second main electrode layer, a second piezoelectric thin film, and a second opposite electrode layer on a second substrate in this order; in the piezoelectric function area, forming these layers into a shape same as the pair of shapes formed on the first substrate, and in the electrode leading area, partially exposing the first main electrode layer formed on the first substrate, and forming a shape in which the pair of shapes are coupled by the second main electrode layer, and the second piezoelectric thin film; opposing and joining the first opposite electrode layer and the second opposite electrode layer to each other using a conductive adhesive layer to form an integrated pair structure; forming an insulating layer for filling a gap in the structure sandwiched between the first substrate and the second substrate; removing the second substrate; forming the insulating layer into a shape such that the insulating layer covers at least an outer periphery of the first main electrode layer; forming a second opening through the insulating layer on the exposed first opposite electrode layer; and forming a connection wiring for connecting to the first opposite layer and leading to a surface layer via the second opening.
 23. The method of manufacturing a thin film piezoelectric element of one of claims 18,19,20 and 22, wherein the insulating layer for filling the gap in the structure is made of photosensitive resin, the method further comprising the steps of: after the liquid photosensitive rein is filled, heat-treating the insulating layer to remove a solvent component in the photosensitive resin; and after etching the insulating layer, further heat-treating the insulating layer at a predetermined curing temperature.
 24. The method of manufacturing a thin film piezoelectric element of one of claims 18,19,20 and 22, wherein each of the first opposite layer and the second opposite layer is made of at least two layers, one selected from Au, Ag, and Cu is formed as an upper layer of one of the first opposite electrode layer on the first piezoelectric thin film and the second opposite electrode layer on the second piezoelectric thin film and one selected from Sn, Cd, Au-containing Sn alloy, and Au-containing Cd alloy is formed as an upper layer of the other of the first and second opposite electrode layers; and in a step of opposing and joining the first opposite electrode layer and the second opposite electrode layer using the conductive adhesive layer, metal films formed as the one upper layer and the other upper layer are heated and alloyed to form the adhesive layer. 